As far as I am aware, formaldehyde usually contains methanol so it does not polymerize. And if my research is correct, methanol is sometimes used to help dissolve phenidone, so it's probably film safe.

I don't recall recipes where Phenidone is (pre)mixed with Methanol, and this page indicates that Phenidone isn't all that soluble in Methanol anyway. That aside, given that Formaldehyde appears to be unstable in its pure form, I would say that most people use the Formaldehyde-Methanol mix, knowingly or not, so the mix should work as expected. Note that commercial prebleach or stabilizer recipes tend to use the Formaldehyde-Bisulfite adduct instead, while C41, according to PhotoEngineer, doesn't need Formaldehyde at all any more.

Formalin, by definition, is 37% formaldehyde. 37% formalin would be 0.12% formaldehyde.

Formalin is another common name for formaldehyde when dissolved in water. It can be used regardless of concentration. If you checked the MSDS listed for that specific product you would see it was consisting of 30.0-50.0 wt% formaldehyde, so to me at least it's clear that it is not 14 wt%. As for what the recipe calls for, I'm not sure. It wasn't specified in the original post whether we were talking v/v or wt%, but I made the assumption we were talking about a 37 wt%, 40% v/v, or "100% formalin" solution. It seems unlikely we would be diluting a 37 wt% solution to 37%.

And I don't know anything about using phenidone first hand, I just read that in an archive somewhere when I was googling the topic. It is capable of forming 10 wt% solutions in methanol if its MSDS is to be believed, though higher concentrations are probably used. Phenidone salts however are unlikely to be soluble in methanol.

It wasn't specified in the original post whether we were talking v/v or wt%, but I made the assumption we were talking about a 37 wt%, 40% v/v, or "100% formalin" solution. It seems unlikely we would be diluting a 37 wt% solution to 37%.

Given that Formaldehyde is a gas, a v/v number is unlikely, so we can safely assume wt%. I do agree that it's extremely unlikely that anyone dilutes a 37% Formaldehyde in water solution down to precisely 37% another time.

Originally Posted by heterolysis

And I don't know anything about using phenidone first hand, I just read that in an archive somewhere when I was googling the topic. It is capable of forming 10 wt% solutions in methanol if its MSDS is to be believed, though higher concentrations are probably used. Phenidone salts however are unlikely to be soluble in methanol.

You may be correct. Here it says "0.1g / ml" which means that the scbt web page likely contains a typo. Given that Phenidone dissolves in water and in Propylene Glycol, I tend to trust the 0.1 g/l number more than the 0.1 mg/l number. I stand corrected.